Enterohemorrhagic

Escherichia coli Infections

Verocytotoxin producing E. coli (VTEC)
Shiga toxin producing E. coli (STEC)
E. coli O157:H7
 Overview
• Organism
• History
• Epidemiology
• Transmission
• Disease in Humans
• Disease in Animals
• Prevention and Control
• Actions to Take
Center for Food Security and Public Health, Iowa State University, 2012
THE ORGANISM
 The Organism
• Escherichia coli (E. coli)
– Gram negative rod
– Family Enterobacteriaceae
– Normal commensals in GI tract
• Enterohemorrhagic E. coli (EHEC)
– Subset of pathogenic E. coli
– Cause disease in humans
– Produce exotoxins

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 Virulence Factors
• Verocytotoxigenic E. coli (VTEC)
– Toxins: Vt1, Vt2
– Also known as shiga toxin-producing
E. coli (STEC)
• EHEC are VTEC that have additional
virulence factors
– Example: genes that produce attaching
and effacing lesions in human GI tract

Center for Food Security and Public Health, Iowa State University, 2012
 Serotypes
• Based on O, H, and K antigens
• EHEC
– O157:H7
– O26, O103, O111, O145
– Others
• Serotyping along cannot
confirm organism as EHEC
– ID of virulence factors required

Center for Food Security and Public Health, Iowa State University, 2012
HISTORY
 History
• First description of E. coli O157:H7
– 1982
– Four patients with bloody diarrhea
– Linked to undercooked hamburgers
at a fast food chain
• Other sources identified over time
• Now a major problem
– Physicians, public health, food industry

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EPIDEMIOLOGY

Center for Food Security and Public Health, Iowa State University, 2012
 Geographic Distribution
• E. coli O157:H7
– Found worldwide
– Exception: Antarctica
• Other EHEC
– Wide distribution
• Prominent serotypes may vary by
geographic area

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 Morbidity and Mortality:
Humans
• Seasonal variation
– North America
• Most infections in summer, autumn
• Due to seasonal shedding in animals or
increase in summer barbecues?
• Incidence
– U.S. 1996-2010: 0.9 cases/100,000
• Mortality
– HUS: 3-10% (children), 50% (elderly)
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O157 Incidence: 1996-2010

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 Morbidity and Mortality:
Animals
• EHEC O157
– Widespread in cattle
– Affected by seasonal variation?
– Prevalence range: 1-36%
– Some animals may be
shedding but not
colonized

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TRANSMISSION
 Transmission in Animals
• Fecal-oral
• Direct contact
• Fomites
– Water troughs
– Shared feed
– Contaminated pastures
• Vectors (birds, flies)
• Aerosol?
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 O157 Reservoirs
• Primary reservoir
– Cattle, sheep
– “Super-shedders”
• Mainly in cattle
• Animals colonized at terminal rectum
• Remain infected for long periods
• May shed more than 95% of E. coli in a herd
• Secondary reservoir
• Humans not a maintenance host
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 Transmission in Humans
• Undercooked or unpasteurized
animal products
– Ground beef**
– Other meats
– Milk, cheese
• Foods contaminated
with feces
– Fruits
– Vegetables
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 Foodborne Outbreaks:
CDC Investigation Examples
• 2012:
– Clover sprouts
• 2011
– Lettuce, bologna, in-shell hazelnuts
• 2010
– Cheese, romaine lettuce, steak
• 2009
– Ground beef, cookie dough

Center for Food Security and Public Health, Iowa State University, 2012
 Transmission in Humans
• Contaminated water
– Private wells
– Municipal water
treatment
usually eliminates
E. coli
– Swimming
(lakes, streams)
• Contaminated soil
– Campgrounds
– Sites grazed by
livestock

Center for Food Security and Public Health, Iowa State University, 2012
DISEASE IN HUMANS
 Disease in Humans
• Incubation
– 1 to 16 days
• Shedding
– 7 to 9 days
– May continue for months
– Longest shedding period in children

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 Disease in Humans
• Hemorrhagic colitis
– Bloody diarrhea
– Severe abdominal cramps
– +/- fever, nausea/vomiting
• Many cases self-limiting
– Resolve in about 1 week

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 Disease in Humans
• Hemolytic uremic syndrome (HUS)
– Children, elderly, immunocompromised
– Usually develops post-diarrhea
• Clinical signs
– Kidney failure, hemolytic anemia,
thrombocytopenia
• Thrombotic thrombocytopenic
purpura (TTP)

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 Diagnosis
• Culture
– Feces, food, environmental samples
– Differential and selective media
– Suspected colonies confirmed with:
• Biochemical tests
• Immunoassays
• Phage typing
• PFGE
• Serology
Center for Food Security and Public Health, Iowa State University, 2012
 Treatment
• Mainly supportive
• Antibiotics
– Usually avoided
– Do not reduce symptoms, prevent
complications, or reduce shedding
– May increase risk of HUS
• Antimotility drugs
– May increase risk of HUS

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DISEASE IN ANIMALS
 Species Affected
• Ruminants (cattle, sheep)
• Pigs
• Rabbits
• Horses
• Dogs
• Raccoons, opossums
• Birds

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 Disease in Animals
• O157:H7 EHEC
– Natural infections
• No illness detected
– Experimental infections
• Disease in very young animals
• Non-O157 EHEC
– Diarrhea, GI signs in young animals
• Shedding
– Subclinically infected, young animals
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 Post Mortem Lesions
• Ruminants
– Inflammation of large intestine mucosa
– Fibrinohemorrhagic exudate
• Other animals
– Hemorrhages
– Kidney failure
resembling HUS
(dogs)

Center for Food Security and Public Health, Iowa State University, 2012
 Diagnosis
• Culture
– Fecal samples, rectoanal swabs
– Differential and selective media
• Detection of antigens, toxins, genes
– Immunological tests
– Nucleic-acid based tests
• Serology not routinely used
in animals

Center for Food Security and Public Health, Iowa State University, 2012
PREVENTION AND
CONTROL
 Recommended Actions
• O157:H7 nationally notifiable
in humans
– Contact your physician for guidance
• Animal cases may be reportable
in some states
– State veterinarian
http://www.usaha.org/stateanimalhealthofficials.
aspx

Center for Food Security and Public Health, Iowa State University, 2012
 Prevention in Humans
• Good hygiene
– Hand washing
• After livestock contact
• Before eating and drinking
• After changing diapers
• Separate contaminated
clothing/linens
• Isolate infected children?

Center for Food Security and Public Health, Iowa State University, 2012
 Prevention in Humans
• Don’t cross-contaminate
– Wash hands, counters, cutting boards,
utensils after contact with raw meat
• Thoroughly cook meats
• Avoid unpasteurized products
• Wash fruits/vegetables before eating
• Keep livestock away from private
water supplies

Center for Food Security and Public Health, Iowa State University, 2012
 Prevention in Animals
• Reduce shedding
– Identify and remove super-shedders
• Pasture rotation
• Vaccination?
• Decolonization?
• Dietary manipulations?

Center for Food Security and Public Health, Iowa State University, 2012
 Additional Resources
• USDA Food Safety and Inspection Service
– www.fsis.usda.gov/wps/portal/fsis/topics/food-
safety-education/get-answers/food-safety-
fact-sheets/foodborne-illness-and-
disease/escherichia-coli-o157h7/ct_index

Center for Food Security and Public

Health
– www.cfsph.iastate.edu

CDC E. coli
– www.cdc.gov/ecoli/
Center for Food Security and Public Health, Iowa State University, 2012
 Acknowledgments
Development of this presentation was made possible
through grants provided to
the Center for Food Security and Public Health at Iowa
State University, College of Veterinary Medicine from
the Centers for Disease Control and Prevention,
the U.S. Department of Agriculture,
the Iowa Homeland Security and
Emergency Management Division, and the
Multi-State Partnership for Security in Agriculture.

Authors: Kerry Leedom Larson, DVM, MPH, PhD, DACVPM; Ariel Pleva, MPH;
Anna Rovid Spickler, DVM, PhD
Reviewer: Glenda Dvorak, DVM, MPH, DACVPM

Center for Food Security and Public Health, Iowa State University, 2012